The electrical transmission of a document between two remote locations initially requires that the information on the document be converted to an electrical signal capable of amplification and transmission to the receiving location whereat the information is used to produce a copy of the original document. At the transmitting location, the document is optically scanned by a light beam the path of which passes through a lens and mirror system. To obtain acceptable resolution of the copy, the characteristics of the light path in the document scanning apparatus must be well defined and predictable. Various structures have been suggested for mounting the scanner components. Such mounting arrangements have been expensive, considerably complicated and unreliable. The mounting and positioning of the mirrors in such a scanner assembly is particularly critical since the reflective surface of the mirror must be precisely positioned with respect to the document and other components of the optical system to obtain the desired resolution in the copy. The mounting of the mirror is particularly difficult since the mirror adjustment and alignment mechanism introduce distortions in the mirror which stresses are relieved or increased when the temperature of the scanner rises during operation. Occasionally the mirrors are mounted using adhesive as the main securing device. This arrangement is particularly unsatisfactory since the characteristics of the adhesive change as it ages resulting in movement of the mirror. Described herein is a mirror mounting apparatus which assures that the mirror will remain accurately positioned over long periods of time and greatly minimizes mirror distortion.